Low Cost Sensor System

ABSTRACT

The invention relates to a low cost sensor array suitable for use in a ware washing machine, preferably a dish washing machine. The invention also relates to a standalone detergent dispensing device comprising the low cost sensor array. The sensor systems are intended to allow monitoring of wash cycles such that controlled sequential dosing of reagents in wash cycles can be optimized. A device comprising such a sensor system may then be able to sense the conditions of the wash and dose reagents in their optimal sequence in the wash.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of and claims priority to U.S. patentapplication Ser. No. 14/759,211, filed 3 Jul. 2015, which is a USNational Stage of International Application No. PCT/GB2014/050051, filed9 Jan. 2014, which claims the benefit of GB 1300362.9, filed 9 Jan.2013, all of which are fully incorporated by reference.

BACKGROUND

In automatic dishwashing machines, the detergent, whether in powder,tablet or gel form, is usually filled manually by the user into themachine, in particular into a detergent holder, before each dishwashingoperation.

This filling process is inconvenient, with the problem of exact meteringof the detergent and possible spillage thereof, for powder and geldetergents. Even with detergents in tablet form, wherein the problem ofaccurate dosing is overcome, there is still the necessity of handlingthe dishwashing detergent every time a dishwashing cycle is started.This is inconvenient because of the usually corrosive nature ofdishwasher detergent compositions.

A number of devices are known for holding unit doses of a detergentcomposition or additive, such as detergent tablets, and for dispensingof such unit doses into a machine.

WO 01/07703 discloses a device for the metered release of a detergentcomposition or additive into a dishwashing machine having a number ofseparate sealed chambers for holding the detergent composition oradditive and means for piercing the chambers, activated by conditionswithin the machine.

WO 03/073906 discloses a free standing device for dispensing multipledoses of detergent into a dishwasher. The device has a plate-likeconstruction. A round blister pack, having a plurality of doses arrangedaround its periphery is loaded into the pack. A winder is then rotatedto load mechanical energy into the device sufficient to dispense morethan one dose of detergent. A thermally operated latch then moves whenthe device is subjected to the elevated temperatures within thedishwasher and, in cooperation with a ratchet mechanism, moves theblister pack so that the next dose of detergent is ready for dispensing.In order to dispense the detergent, either the blister pack is pierced,or the dose is ejected from its compartment within the blister pack.

WO 03/073907 discloses a similarly shaped free standing dispensingdevice. In order to dispense detergent, a lever is manually operated tomove a blister pack either to eject the detergent from a compartmentwithin the blister pack, or to pierce the blister pack. A door or flapinitially prevents wash liquor within the machine from accessing theexposed detergent. A bi-metallic strip is provided to move the door orflap when the device is exposed to the elevated temperatures during awashing cycle to allow access of the wash liquor to the exposeddetergent thereby dispensing the detergent to the machine.

WO2006/021769 relates to an automatic detergent dispensing device thatis reactive to temperature changes in the dishwasher.

The prior art devices all react to a simple input from the washconditions. Normally heat.

WO2005/011462 relates to improved detergent dosing in automatic machinedishwashing. The contents of which are herein incorporated by reference.

This patent discloses the benefits of controlled sequential dosing oftreating agents within detergent compositions. The different treatingagents within detergent compositions are also often mutuallyincompatible and interfere with each other, for example the enzymes andthe bleach components of most automatic machine cleaning detergents. Thecontrolled sequential dosing is enabled through the use of sensorsconnected to the washing machine.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying Figures, which are incorporated in and constitute apart of this specification, illustrate several aspects described below.

FIG. 1 shows the resulting characteristic of forward voltage againsttemperature for a typical LED of each of green, red and yellow.

FIG. 2 depicts a front perspective view of an exemplary standalonedetergent dispensing device 14, according to some embodiments of theinvention, comprising an exemplary sensor system 11 according to someembodiments of the invention.

FIG. 3 depicts a front view of an exemplary standalone detergentdispensing device 14, according to some embodiments of the invention,comprising an exemplary sensor system 11 according to some embodimentsof the invention.

FIG. 4 depicts a rear view of an exemplary standalone detergentdispensing device 14, according to some embodiments of the invention,comprising an exemplary sensor system 11 according to some embodimentsof the invention.

DETAILED DESCRIPTION OF THE INVENTION

It is the object of the present invention to provide a sensor systemthat would be suitable for use in an automatic washing machine.

In a first aspect of the present invention there is provided a sensorsystem 11 that is suitable for use inside a ware washing machine thatcomprises at least one semiconductor 12, preferably a diode.

The present invention is related to the development of sensor systemsfor use in ware washing machines. The sensor systems are intended toallow monitoring of wash cycles (e.g., by monitor 13) such thatcontrolled sequential dosing (e.g., by controller 19) of reagents inwash cycles can be optimised.

It is preferable that the sensor system is machine independent. By thisit is meant that it is preferable that the sensor system can be used indifferent machines. Therefore it is preferable that the sensor systemcan correctly interpret wash cycle conditions over a wide range ofdifferent wash cycles in different types of machine.

It is the second aspect of the present invention to provide a standalonedetergent dispensing device 14 comprising the sensor system 11 of thefirst aspect of the invention. The device may then be able to sense theconditions of the wash and dose reagents in their optimal sequence inthe wash.

In particular the invention relates. It is the object of the presentinvention to provide a more sensitive device capable of reacting tosubtle changes in the wash conditions.

Preferably the device will be able to dose the quantities of thedifferent reagents in response to the sensorial feedback from the sensorsystem 11 (e.g., the reagents may be dispensed from a dispensing pump 15or a dosing mechanism 17).

Thus by way of non-limiting example, If turbidity levels are high thedetergent dispensing device may release more detergent. To be effective,the device may require software (e.g., in a hardware element 18) toanalyse the sensor input and to control the necessary response.

Alternatively it may release set amounts of reagents at specified pointsin the wash cycle.

Such a device will require a power supply 20. This may be in the form ofbatteries. Alternatively the device may draw energy from the conditionsin the washing machine. These can be heat or motion for example.

Preferably however, the device will use batteries for power.

Because battery power is necessarily limited, sensor power consumptionmay be important. As will be the mechanism by which the detergent willbe dispensed from the device.

For the purposes of the present application any reference to sensorsystem may apply to the first aspect of the present invention (thesensor system) or to the second aspect of the present invention (adetergent dispensing device comprising the sensor system of the firstaspect).

The sensor system 11 needs to be accurate, monitor multiple parameters,be robust enough to survive the conditions of the ware washing machineand be of sufficiently low cost to make it commercially viable.

The sensor system preferably needs to be simple and use the smallestnumber of sensors to measure the largest number of parameters.

As the sensor system of the present invention is preferably able to workwith a standalone detergent dosing device that is capable of being usedin a variety of automatic cleaning machines, it must be capable ofdetecting several different conditions for determining optimalconditions for dosing.

The physical conditions that would be highly desirable to monitor are:

-   1. Presence or absence of water.-   2. Presence or absence of light (to determine if the dishwasher door    is open).-   3. Water temperature.-   4. Rate of change of water temperature.-   5. Water turbidity.

The ability to detect the presence or absence of water will allow thesensor system to determine whether or not the machine is currently in awash cycle or waiting for use.

The ability to detect light and dark will allow the sensor system todetermine whether the dishwasher door is open or closed. This will beimportant for determining whether or not dosing should be carried out.

The ability to detect water temperature and the rate of change of thewater temperature will allow the sensor system to determine what stageof the wash cycle has been reached. For example, most wash programsbegin with a cool prewash. The sensor array needs to be able todetermine this to be able to know when to dose certain ingredients.

Water turbidity is another useful parameter. This is useful to determinewhether more reagents need to be added to the wash liquor for aneffective clean.

A workable sensor system can be effective that monitors at least threeof these parameters. To provide the most sensitive and widely applicablesensor system preferably at least four of these parameters will bemonitored and most preferably all five.

Other conditions such as pH level, motion sensing, water hardness etccan also be monitored if desired. These additional sensors may be addedto the sensor system of the present invention as desired. The presentinvention is not limited to the five suggested parameters above.

The sensor system may monitor six or more parameters, preferably sevenor more parameters and most preferably eight or more parameters.

At its most simple the present invention would involve the use of asingle semiconductor as a sensor system to monitor many conditionswithin the wash cycle.

The applicants have found that semi-conductor sensors are particularlydesirable for use in sensor systems of the present invention.

Semi-conductors are extremely cheap and robust, properties that makethem highly effective sensors for the machine cleaning environment.

At its most basic the present invention would involve at least onesemiconductor sensor 12 in a sensor system 11.

The preferred type of semi-conductor for the purposes of the presentinvention are diodes.

The preferred type of diode are LEDs. (Light emitting diodes) The LEDmay be an infrared light emitting diode.

In a further embodiment the sensor system of the present invention wouldcomprise at least two semiconductor sensors. These may both be forms ofdiode. Alternatively at least one may be a diode.

In a further embodiment the sensor system of the present invention wouldalso comprise a pair of capacitance plates 16. These can be used todetect when the automatic washing machine is filled with water.

In a further embodiment the capacitance plates 16 could be used assensors independently of the diode sensors 12. The capacitance plates 16may be combined with other sensors to provide a different sensor system.

In a further embodiment the sensor system of the present invention mayalso comprise further sensors. Non-limiting examples may include pHsensors, motion sensors and thermistors. These sensors may be used toadd new and different capabilities to the sensor system or improve theperformance of previously monitored parameters.

A single semiconductor sensor, preferably a diode, may be able to detectthree of the five preferred conditions above. These may be, the presenceor absence of light (to determine if the dishwasher door is open), watertemperature and rate of change of water temperature.

The diode may be an light emitting diode (LED). The LED may emit lightacross the frequency band. The LED may emit frequencies outside thevisible spectra. In particular infrared emitting diodes are effective.

With an additional semiconductor sensor, which is preferably also adiode, the sensor system may also be able to monitor the water turbiditylevels within a ware washing machine (e.g., in conjunction with amonitor 13). The second diode may also be used to provide greatersensitivity to the measurements of light levels and water temperature.

With the addition of capacitance plates 16, the sensor system will beable to detect water presence.

In a preferred embodiment the sensor system would comprise an LED, aphoto detector and capacitance plates.

Preferably the LED would be an infrared emitter, the photo detectorwould be a photodiode or a phototransistor.

Parameter: Measured by: Water turbidity Infrared emitter (LED) andinfrared detector (photodiode or phototransistor) Water temperature Sameinfrared emitter as used for turbidity measurement Ambient light Sameinfrared detector as used for turbidity measurement Water presenceCapacitance plates

This preferred arrangement of sensors would require the use of only twosemiconductor sensor components, plus a simple pair of capacitiveplates. The capacitive plates even may simply comprise exposed trackingon a circuit board 18 adjacent an external wall of the device.

The preferred sensor system would use a LED to detect temperature. Thelight detector preferably comprises and phototransistor, (LED orphotodiode would also work) and would be used to monitor turbidity andambient light. Capacitance plates would be preferred to detect water.

This combination would allow enough parameters to be measured for thepreparation of the sensor system capable of working with a wide range ofdifferent machine types.

Sensors may be internal or external the device. External placementallows for rapid sensing but offers increased risk of leakage into thedevice. Internal placement allows for protection against the harshenvironment of the dishwasher (highly alkaline wash liquor) but mayreduce sensitivity, time lag for temperature sensing for example.

A preferred option may be to place the sensors behind a thinned sectionof the device outer wall. To achieve this the wall can be made of amaterial that allows transmission of certain wavelengths of light andtemperature. For example biaxially orientated polypropylene would allowthe transmittance of light sufficient for successful LED and detectorsensors. The capacitance plates would also function when placed behindthe wall.

Preferably the sensors would be behind an external wall with a thicknessno greater than 4 mm, more preferably no greater than 3 mm thick, morepreferably no greater than 2 mm thick and most preferably no greaterthan 1 mm thick.

Treatment Compositions

The device of the present invention may have single treatmentcompositions to dose. However, preferably the device of the presentinvention may have two or more different treatment compositions to dose.

More preferably the device would have at least three differentcompositions, more preferably at least four different treatmentcompositions and most preferably at least five different treatmentcompositions to sequentially release.

Non-limiting examples of different treatment compositions that may beincluded within the device for controlled sequential release may includebe a water softening or builder composition, an enzyme composition, asurfactant composition, a bleach composition, a perfume composition,drying or rinse aid composition, or combinations thereof.

The treatment compositions may be in discrete amounts for dosing. Thedevice may dose in multiples of the discrete amount of treatmentcomposition only (e.g., from a dispensing pump 15 or a dosing mechanism17). Alternatively and preferably the treatment compositions may bemetered in controlled amounts (e.g., by a controller 19) according tothe output from the sensor system.

The treatment compositions may be in liquid or solid form for metereddosing (e.g., from a dispensing pump 15 or a dosing mechanism 17). Thepreferred form for the treatment compositions of the present inventionare liquids. This is because liquids are easy to measure and dispenseand given the high humidity environment inside automatic cleaningmachines powdered solids are extremely likely to cake and blockdispensers.

EXPERIMENTAL

Measuring Temperature Via a Diode Sensor:

The key parameter of operation of most types of diode (includinglight-emitting types) which is sensitive to temperature is the forwardvoltage due to a fixed current. It is this parameter which was examined.

The LEDs were electrically insulated and arranged so that they wereconnected to a driving circuit using thin wires having a negligiblethermal capacity and high thermal resistance. They were then placed inan oil bath having an accurately controlled temperature control system.Precautions were taken to ensure uniformity of temperature distributionthroughout the oil bath.

A constant DC forward current of 1 mA was passed through each LED andthe forward voltage in each case was examined and recorded for each of anumber of oil bath temperatures. The current of 1 mA was selected so asto have a negligible self-heating effect upon the LEDs.

The temperature of the bath was recorded using a thermocouple placed inclose proximity to the LEDs. The LED forward voltages and oiltemperature was recorded for temperatures of between 37° C. and 100° C.in approximately 0.2° C. intervals.

The resulting characteristic of forward voltage against temperature fora typical LED of each colour is shown in FIG. 1.

The observed characteristics of forward voltage are extremely linear,having similar gradients and with differing offsets as would be expectedfor LEDs of differing colours.

The infrared LED emitter was evaluated in a similar manner to that usedfor visible LEDs using a fixed forward current of 1 mA and measurementof the forward voltage as temperature is varied. As anticipated astraight line characteristic of forward voltage against temperature wasevident which exhibited a gradient of −1.8 mV/° C. and with a voltagevalue at 25° C. of 0.938V.

This result is broadly similar to those obtained for visible LEDs exceptfor a downward shift in the entire characteristic (approximately from1.4-1.9 volts to 0.9 volts). This is as anticipated and ischaracteristic of an LED optimised for infrared operation. The testshave shown that the use of an LED as described results in an extremelylinear temperature measurement technique. Thus a single LED can make ahighly effective temperature sensor.

Detection of an Ambient Light Threshold Using a LED.

Test were undertaken using samples of each of three randomly selectedLEDs, one red, one green and one yellow. These were all general purposeLEDs with conventional 3 mm leaded packages. Because the ambient lightmeasurement is intended to indicate whether the door of the dishwasheris open or closed, two illumination conditions were defined which wererepresentative of the worst-case door-open and door-closed states.

These were as follows:

-   Door open: Illumination level occurring at the back of the top rack    of a dishwasher with the door open and with only relatively poor    illumination in the surrounding room. This corresponded to an    illumination level of approximately 2 lux.-   Door closed: Illumination level occurring anywhere within a    dishwasher with the door closed. This corresponded to an    illumination level of 0 lux.

The chosen mode of operation of the LED was as a reverse-biasedphotoconductive device. The alternative photovoltaic configuration wasnot evaluated because the extremely low voltages generated at the lowillumination levels would require the use of a prohibitively expensivecircuit configuration.

The LED under test had a reverse bias of 5 volts applied and theresultant reverse current was measured using an Agilent 4329A femtoammeter. This series of tests was performed at an ambient temperature of20° C. The currents corresponding to the door closed and door openconditions were recorded for each colour of LED and are shown in thetable below.

current for each condition: Current ratio LED colour Door closed Dooropen (open:closed) Red 20 pA 3 nA 150:1  Green 78 pA 620 pA 8:1 Yellow160 pA 1.45 nA 9:1

Further tests were undertaken to identify any significant difference inresistance in the Door open condition due to differences in the spectraof ambient light from tungsten or fluorescent light sources. In generalterms the red LEDS appeared to be approximately equally sensitive to thetwo types of lighting whilst the green and yellow LEDs appeared to beapproximately 20% less sensitive to tungsten lighting than tofluorescent lighting.

Improved Sensitivity

The infrared phototransistor was evaluated in a similar manner to thatused for visible LEDs using the previously defined Door open and Doorclosed conditions.

The mode of operation of a phototransistor is slightly different fromthat of a photodiode but still results in a variable current accordingto the level of illumination. The results obtained at 20° C. are asfollows:

Current for each condition: Current ratio Door closed Door open(open:closed) <1 nA 180 μA 180000:1

This result is substantially improved over that obtained with visibleLEDs. Although not tested, it is known that the dark current willincrease approximately by a factor of 2 for every rise in temperaturethrough an increment of 10° C. Therefore in a worst-case condition oftemperature rise of 60° C. (from 20° C. to 80° C.) an increase in Doorclosed current of 1 nA×26=64 nA. This case would result in a reducedDoor open to Door closed current ratio of 2800:1. Again this representsa substantial improvement over the use of visible LEDs.

Water Turbidity

It is quite possible using appropriate circuitry that a conventionaloptical LED may be used to perform the function of a photodetector—thatis as a light detector. It is also possible that an LED may alternatebetween being used as an emitter and a detector.

The possibility therefore exists that an LED used in the sensor systemmay serve a secondary purpose as one of the photodetectors which may berequired. Perhaps the most obvious area where such a doubling-up offunctionality may be achieved is by using a user LED (ie one intended toconvey information to the user) as the ambient light detector. Howeverthe increased complexity of the circuitry required to implement the dualfunctionality could conceivably result in an overall cost which isgreater than if a separate LED and photodetector were used.

Water Presence—Use of Capacitive Plates

The essence of this technique is to create a variable capacitance formedby a pair of conductive elements housed within the dry conditions in thecasework of a sensor system and placed immediately adjacent to theinside wall of the casework. Under conditions of water absence thecapacitance between these elements is extremely low. Under conditions ofwater presence outside the unit, the capacitance between the elementswill rise. This is due to the creation of a pair of effective capacitorsin series, one between the first element and the water, and the otherbetween the second element and the water.

A simple capacitance-dependent technique was devised which relies uponplacing an initial charge upon the capacitor formed by the twoconductive elements and then measuring how long the capacitor takes todischarge through a known resistor. This time period indicates themagnitude of the capacitance.

Simple Capacitive Plate Embodiment

A first embodiment consisted of a pair of metal plates each havingdimensions of approximately 3 mm×3 mm. These were placed approximately 1mm apart in contact with the inner surface of an ABS wall section ofvariable thickness. Tests were undertaken with the outside of this wallbeing either dry or irrigated with water to a depth of at least 0.5 mm.

The approximate ratios of capacitance of this arrangement between thewet and dry conditions with various thicknesses of ABS wall were asfollows:

Capacitance ABS thickness wet:dry ratio 0.5 mm 10:1  0.8 mm 5:1 1.6 mm2:1

Any increase in depth of water over approximately 0.5 mm resulted in nosignificant improvement in the capacitance ratio. The use of ABS inthese tests was simply due to the availability of suitable sheetmaterial. ABS has a similar but slightly higher relative permittivitythan polypropylene and so the capacitance ratios which might be obtainedwith a polypropylene wall are likely to be broadly similar to thoseshown above. Because of the high impedance nature of the circuit used inthese tests, there was no significant difference in measurements madeeither using distilled water or sodium chloride solution.

What is claimed is:
 1. A sensor system suitable for use inside a warewashing machine that comprises at least one semiconductor.
 2. The sensorsystem of claim 1, wherein the sensor system comprises at least twodiodes.
 3. The sensor system of claim 2 further comprising a pair ofcapacitive plates.
 4. The sensor system of claim 1, wherein the at leastone semiconductor is a light emitting diode.
 5. The sensor system ofclaim 4, wherein the light emitting diode is an infrared emitting diode.6. The sensor system of claim 1 configured to detect at least threedifferent physical parameters in a ware washing machine.
 7. The sensorsystem according to claim 6, wherein the parameters are selected fromthe group consisting of wash water turbidity, wash water temperature,light level and water presence.
 8. The sensor system of claim 1 furthercomprising at least one additional sensor selected from the groupconsisting of thermistors, photo-resistors, photo transistors, pHsensors, pressure sensor, movement sensor, conductance sensor andcombinations thereof.
 9. The sensor system according to claim 1 furthercomprising software and processing power configured to interpret sensorsignals.
 10. A standalone detergent dispensing device, suitable for usein a ware washing machine, comprising the sensor system of claim
 1. 11.The standalone detergent dispensing device according to claim 10 furthercomprising a power supply and a dispensing apparatus to releasetreatment compositions in response to inputs from the sensor system. 12.The device according to claim 11, wherein the device has two or moredifferent treatment compositions to release.
 13. The device according toclaim 11, wherein the device has three or more different treatmentcompositions to release.
 14. The device according to claim 11, whereinthe device has four or more different treatment compositions to release.15. The device according to claim 12, wherein the treatment compositionsare selected from the group consisting of enzyme reagents, bleachreagents, surfactant reagents, rinse aids water softening reagents andmixtures thereof.
 16. The device according to claim 12, wherein a doseof each treatment composition can be controlled and metered in responseto sensory input from the sensor system.
 17. The device according toclaim 12, wherein a dose of each reagent is fixed in response to adefined sensory input from the sensor system.
 18. The sensor system ofclaim 1 configured to detect at least four different physical parametersin a ware washing machine.
 19. The device according to claim 17, whereinthe sensor system further comprises a pair of capacitive plates and isconfigured to detect at least three different physical parameters in thedevice.